A contactless power transfer device includes a contactless power transfer transformer having a power transmission coil (primary coil) and a power receiving coil (secondary coil) and a capacitor connected to the power transmission coil and the power receiving coil and supplies power from the power transmission coil to the power receiving coil by using electromagnetic induction between the power transmission coil and the power receiving coil.
A contactless power transfer system including the contactless power transfer device includes a high-frequency power source that supplies high-frequency AC to the power transmission coil of the contactless power transfer device and a secondary rectifier that converts AC transmitted to the power receiving coil of the contactless power transfer device into DC. In a contactless power transfer system for charging a vehicle, the power transmission coil connected to the high-frequency power source is installed in the ground of a power transfer station, the power receiving coil is mounted on a lower surface of a floor of the vehicle, and high-frequency AC induced in the power receiving coil is rectified by the secondary rectifier installed in the vehicle and charges a secondary battery in the vehicle.
In the case of a contactless power transfer device for charging a vehicle, a positional deviation in the horizontal direction and a gap length variation in the vertical direction between the power transmission coil and the power receiving coil easily occur. If power is transferred with a large positional deviation left unchanged, it causes problems that the power transfer efficiency significantly degrades, the lower surface of the floor of the vehicle near the power receiving coil is heated, the strength of magnetic flux that leaks to the outside of the vehicle increases, and so on.
Therefore, in the contactless power transfer system for charging a vehicle, an acceptable range of the positional deviation between the power transmission coil and the power receiving coil in the front-rear direction, the left-right direction, and the up-down direction are determined, and the vehicle to which power is transferred is requested to be parked so that the power receiving coil is inside the acceptable range with respect to the power transmission coil.
The acceptable range (power transferable range) is set, for example, as illustrated in FIG. 20 by considering convenience of parking, prevention of adverse effects of magnetic flux leakage due to positional deviation, restriction of variation range of voltage ratio between the primary and the secondary voltages, and so on. In FIG. 20, the power transmission coil is represented by reference numeral 3, the power receiving coil is represented by reference numeral 5, and the acceptable range of the center P of the power receiving coil 5 with respect to the center O of the power transmission coil 3 is represented by D.
In the front-rear direction (x direction), a positional deviation up to 45 mm from a normal state (positional deviation is 0) is acceptable.
In the left-right direction (y direction), a positional deviation up to 150 mm from a normal state (positional deviation is 0) is acceptable.
In the up-down direction (z direction), a positional deviation up to 30 mm from a normal state (gap length is 70 mm) is acceptable.
In FIG. 20, the z direction component (length) of the line segment OP represents a mechanical gap between the power transmission coil and the power receiving coil.
In a power transfer station for buses in Europe, as illustrated in FIG. 21A, a method is employed in which a concrete block 72 is arranged on a road shoulder where the power transmission coil 3 is installed in the ground and a bus stops at a position with no positional deviation by causing a tire 71 to slide on the concrete block 72. In the up-down direction, as illustrated in FIG. 21B, it is designed so that an appropriate gap length is obtained when the power receiving coil 5 is lowered and comes into contact with the ground through a spacer 73.
In Patent Literature 1 below, as illustrated in FIG. 22, a contactless power transfer device is disclosed in which, the power transmission coil 3 and the power receiving coil 5 are formed by a coil (one side winding coil) in which a winding wire is arranged on one surface of a core, communication coils 15 are disposed at the centers of the power transmission coil 3 and the power receiving coil 5, and when communication sensitivity between the communication coils 15 reaches a certain level, it is determined that the power transmission coil 3 and the power receiving coil 5 enter the power transferable range.
As a circuit system of the contactless power transfer, various methods disclosed in Patent Literature 2 and Non-patent Literatures 1 and 2 below are known as described later.